When the alarm sounds at 7:00am, and you painstakingly ease yourself out of bed, the sight of the pet cat or dog, sprawled out in blissful slumber is hard to bear. Being able to sleep as freely as that would be a dream (no pun intended) for sure, but realistically, if any of us did rest as much as they did — approximately 12.5 hours a day for cats and 10 hours for dogs — we would be low on energy, lethargic and slow to catch on to the day’s routine. Yet neither cats or dogs are oversleeping when they stretch out for more than half the day. They’re getting just the right amount their little furry bodies need.
Rest is essential and all animals engage in some sleep-like cyclical behavior. How each goes about it, however, is wildly diverse. Some shut off only part of their brain when they conk out, while others sleep for extremely long periods of time to conserve energy. Others are, well, just weird (here’s looking at you, cuttlefish). From Lemon Sharks to Little Brown bats, here are some of the more unique sleep habits in the animal kingdom.
Despite the obvious differences in physiology and lifestyle, honeybees actually have a circadian rhythm, or biological clock, close to that of mammals. And although the definition of sleep is hazy at times, bees do engage in sleep-like behavior characterized by immobility, drooping downwards and delayed response to external stimuli. They also function poorly when they don’t get enough of it. Sound familiar?
Little Brown Bat
The little brown bat is a champion of sleepers in the animal kingdom. One of the most common bats in North America, these little guys snooze for an average of 19.9 hours a day. Though it seems indulgent, the extended sleep time is actually a maximized use of energy. The few hours of the day they’re not huddled together upside down in a roost, they’re engaged in aerial battles of the night, hunting their insect prey on the wing. Those few extra Zzz’s give them the juice needed to come back to the cave with a full stomach.
Nematode C. elegans
The transparent nematode Caenorhabditis elegans lacks respiratory and circulatory systems yet still exhibits some form of sleep-like behavior. After each molt, the 1mm roundworm slips into periods of lethargy that are thought to help develop its neural networks. So far, it is one of the most primitive organisms known to sleep (or something like it).
Like all reptiles, alligators are heteropathic, otherwise known as cold blooded, and spend significant portions of their day basking in the sun to conserve energy and keep their body temperatures up. And while this is most certainly rest, it doesn’t necessarily involve sleeping. Alligators, along with other reptiles, do slip into true sleep, but it’s up in the air as to whether they experience REM sleep, a tenant of mammalian shuteye.
Rodents tend to sleep longer and deeper than their larger mammalian counterparts because they’re often tucked away into safe hiding. Rats, for example, sleep about 12.6 hours a day, albeit off and on, in between snagging pizza slices off subway station staircases. Like other mammals and some birds, rats also experience REM sleep, the stage of sleep where dreaming occurs. In captivity, the bald tailed critters have been observed dreaming of mazes — and sniffing out the reward at the end of it.
Cuttlefish are currently the only known invertebrates to possibly experience two stages of sleep. The color changing cephalopods — relatives of octopuses and squid — have highly sophisticated and complex brains that may play a role in this. In studies, they’ve been observed jiggling their tentacles, feverishly flashing their color changing skin, and possibly flitting their eyes around, despite being otherwise motionless. If it is indeed REM sleep, cuttlefish could perhaps provide clues to the evolution of sleep cycles in complex organisms.
To solve the major problem of offering up oneself on a platter for predators while sleeping, birds have evolved an ability known as unihemispheric sleep. In this state, one half of the brain shuts off, even dripping into REM sleep; the other half, meanwhile, stays awake and responsive to stimuli.
When snoozing this way, birds will literally sleep with one eye open and can control how “asleep” their brain gets by how wide they keep their lid open. Mallard ducks doze in groups on the ground, so individuals lying on the outer edges of these avian cliques keep their brains the most awake, in order to better spot potential predators and arouse the others.
Though certainly capable of unihemispheric sleep like most birds, bald eagles are likely less required to do so. These large raptors are the hunters, not the hunted, so they don’t really need to worry about getting snatched while catching some shut eye. They do need to worry about falling out of trees, however. The solution: special muscle mechanisms in their feet allow them to lock their talons in place. This way they can wind down without taking a nasty tumble.
If there is any animal that can sleep wherever it wants, and as conspicuously as it wants, it is the king of the jungle. Such is the luxury of being an apex predator. A stretched-out lion, with fuzzy belly shamelessly raised up toward the sun, is the epitome of bliss and relaxation.
Yet their 13.5 hours of daily sleep serve a crucial purpose like every other creature on Earth: to store up caches of energy for the explosive muscle straining exertions needed to bring down large prey. Carnivores generally get more sleep than herbivores because their meaty meals tend to have a much higher caloric content. An elephant, for example, must spend almost all day eating shrubs and roots to reach the caloric requirement needed for its massive body.
Contrary to popular belief, not all species of sharks need to keep swimming to stay alive. “While it’s true for many species of sharks, many more don’t have to,” says Alan Henningsen, fishes research specialist at the National Aquarium in Baltimore. Lemon sharks, for example, are facultative swimmers, meaning they can swim or stay put, and use that ability to rest on the bottom at times.
Whether they decide to put the brakes on or not depends on the situation, however, because they actually use more energy staying still. The muscles around their head must actively pump water and oxygen across their gills in order to breathe. For sharks that do need to stay moving, it’s believed that the spinal cord may control swimming over the brain, keeping them mobile, while allowing the brain to power down a little bit.